1. Field of the Invention
This invention relates to .alpha.-cyano-3-phenoxybenzyl 2-(4-substituted-phenyl)isovalerates having a high insecticidal and acaricidal activity and a process for preparing the same. More particularly, the present invention relates to .alpha.-cyano-3-phenoxybenzyl 2-(4-substituted-phenyl)-isovalerates which consist substantially of or are rich in the enantiomer pair (S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-substituted-phenyl)isovalerate and (R)-.alpha.-cyano-3-phenoxybenzyl (R)-2-(4-substituted-phenyl)isovalerate.
The compounds to which the invention is directed are .alpha.-cyano-3-phenoxybenzyl 2-(4-substituted-phenyl)isovalerates of the formula (I): ##STR1## wherein X is hydrogen, Cl or F; R is Cl, F, hydrogen, lower alkyl or lower haloalkyl; Z is oxygen or sulfur; and n is 0 or 1, with the proviso that when n is 0, then X is not hydrogen. These compounds have a low toxicity to mammals and a broad range of insecticidal and acaricidal activity. For example, the compound fenvalerate wherein X is Cl and n is 0 is disclosed in Japanese Patent Application (OPI) No. 26425/74 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and U.S. Pat. No. 3,996,244. The compound wherein X is F; R is H, Z is O and n is 1 (difluoromethoxy) is disclosed in British Pat. No. 2017688A published Oct. 10, 1979.
The invention is particularly directed to compounds of the formula (II): ##STR2## wherein X.sup.1 is Cl or F; R.sup.1 is hydrogen, methyl or methyl substituted with F; and n is 0 or 1, with the proviso that when n is 1, X.sup.1 is F.
Each compound of formulas (I) and (II) contains two asymmetric carbon atoms in the molecule (designated by an asterisk (*) in the formula) and, therefore, includes four optical isomers.
In this specification, .alpha.-cyano-3-phenoxybenzyl 2-(4-substituted-phenyl)isovalerate and its isomers will be identified as follows: .alpha.-cyano-3-phenoxybenzyl 2-(4-substituted-phenyl)isovalerate of the formulas (I) and (II) above will be referred to hereinafter as "substituted phenylisovalerate", or "S phenylisovalerate"; (R, S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-substituted-phenyl)isovalerate will be referred to as "S phenylisovalerate A"; (S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-substituted-phenyl)isovalerate will be referred to as "S phenylisovalerate A.alpha."; (R)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-substituted-phenyl)isovalerate will be referred to as "S phenylisovalerate A.beta."; (S)-.alpha.-cyano-3-phenoxybenzyl (R)-2-(4-substituted-phenyl)isovalerate will be referred to as "S phenylisovalerate B.alpha.", (R)-.alpha.-cyano-3-phenoxybenzyl (R)-2(4-substituted-phenyl)isovalerate will be referred to as "S phenylisovalerate B.beta."; the enantiomer pair consisting of a mixture of S phenylisovalerate A.beta. and S phenylisovalerate B.alpha. will be referred to as "S phenylisovalerate X"; and the enantiomer pair consisting of a mixture of S phenylisovalerate A.alpha. and S phenylisovalerate B.beta. will be referred to as "S phenylisovalerate Y". Y-rich and X-rich S phenylisovalerates will be used to designate S phenylisovalerate mixtures rich in S phenylisovalerate Y and S phenylisovalerate X, respectively. In the case where the 4-substituent on the phenyl group is chloro, to designate the specific compound the term fenvalerate will be used instead of S phenylisovalerate.
The relationship between the absolute configurations of the asymmetric carbon atoms in the acid moiety and alcohol moiety to the insecticidal and acaricidal activity of the compounds has already been reported. The following references describe fenvalerate A.alpha., having (S)-configurations at the asymmetric carbon atoms on both acid and alcohol moieties, as the most active stereoisomer of the four. Japanese Patent Application (OPI) No. 24019/78 (corresponding to U.S. Ser. No. 825,570, filed Aug. 17, 1977); Japanese Patent Application (OPI) No. 59646/78; Ohno et al., J. Pesticide Science, 2 (Special Issue), December 1977; and Aketa et al., Agr. Bio. Chem. 42, 895 (1978). The British Patent Application No. 2017688A shows that the isomers of S phenylisovalerate wherein the phenyl substituent is difluoromethoxy having (S)-configuration at the acid asymmetric carbon atom and being racemic at the corresponding alcohol carbon are more active than the full racemate. U.S. Pat. No. 4,176,195 discloses fenvalerate Y as a highly active pesticide.
In the case of esters of .alpha.-cyano-3-phenoxybenzyl alcohol and a dihalovinylcyclopropanecarboxylic acid, for example, cypermethrin (NRDC-149), i.e., .alpha.-cyano-3-phenoxybenzyl 2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylate, and .alpha.-cyano-3-phenoxybenzyl 2,2-dimethyl-3-(2,2-dibromovinyl)cyclopropanecarboxylate, the (S)-isomers of the alcohol moiety in the esters are more active than the (R)-isomers thereof. Racemization (or epimerization) of .alpha.-cyano-3-phenoxybenzyl esters of d-cis-2,2-dimethyl-3-(2,2-dibromovinyl)cyclopropanecarboxylic acid and d-cis-2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylic acid in the presence of a basic catalyst has been reported and, furthermore, (S)-isomer esters of the alcohol moieties have been obtained from the ester having (R,S)-alcohol and d-cis isomer of these dihalovinylcyclopropanecarboxylic acids as described in Belgian Pat. No. 853,866 (and Belgian Pat. No. 853,867 (1977).
Although these patents claim the "chiral acid" ester, in the examples, only cases of d-cis-dihalovinylcyclopropanecarboxylic acid esters are shown. Particularly, in the latter case, the patent requires that one stereoisomer of a diastereomer pair must crystallize selectively from the solution of the mixture with the other diastereoisomer of the pair; therefore every "chiral acid" ester stereoisomer cannot be obtained.
In the case of fenvalerate, the epimerization of the alcohol moiety of the optically active fenvalerate and processes for obtaining fenvalerate A.alpha. fenvalerate A by a selective crystallization or crystallization combined with concurrent epimerization have been applied for in U.S. Application Ser. No. 922,476, filed July 7, 1978 (corresponding British Patent Specification No. 2001964A, published Feb. 14, 1979. However, in these methods for obtaining fenvalerates, optical resolution of the carboxylic acid is necessary in the synthesis of fenvalerate A; for example, these resolution methods involve reaction with an optically active base, selective crystallization of the resulting diastereomer salt, purification of the salt and decomposition of the salt to obtain the optically active carboxylic acid. Furthermore, for economy the enantiomeric acid by-product must be reused, for example, after racemization. On the other hand, the racemization of the useful optically active acid or derivatives thereof must be avoided and, as a result, the reaction conditions are limited.